The present application relates to an improved apparatus and method for hip replacements, and more specifically to a less-invasive prosthetic which replaces the femoral head while retaining the natural femoral neck.
A widely used design for replacement of the proximal portion of a femur employs an elongate, often curved, shaft that extends into the medullary canal of the femur. This design has the tendency to place unnatural stresses on the femur which lead to pain and the consequent curtailment of activity for the patient. Further, present techniques can lead to proximal bone loss and call for the resection of the majority of the femoral neck. Current designs also call for fixing the prosthesis in the proximal third of the femur. The useful life of an intramedullary implant is often less than the expected life span of a young patient.
Previously known prostheses for replacing a femoral head that do not extend into the medullary canal have been mechanically complex or have proven troublesome in actual use. Huggler, U.S. Pat. No. 4,129,903 and Grimes, U.S. Pat. No. 4,795,473 are examples of prosthetic implants having a side plate attached to the exterior lateral side of the femur opposite the femoral head. Screws are used to secure the plate to the femur and one or more holes are drilled into the femur for securing the plate to the bone. The additional holes and the stresses at the site of fixation are believed to cause trauma to the bone.
Masini, U.S. Pat. No. 5,571,203 discloses a device having a shaft that extends through a resected portion of the proximal femur, positioned co-axially relative to the longitudinal axis of the femur. The device is secured by a screw or similar locking device that extends into the femur from the lateral side, just below the greater trochanter. It is believed that the natural forces applied to the prosthesis during normal hip motion result in the application of shear forces to the greater trochanter. The shear forces can be harmful to the greater trochanter and can permit micro-movement of the prosthesis on the unsecured side.
A conventional method for implanting the above types of femoral head implants is described in Campbell""s Operative Orthopaedics, (Mosby, 7th ed., 1987) and typically includes making a large incision in the patient""s lateral side at the hip joint and through the skin and muscle, dislocating the hip and then sawing off the femoral head. This method is considered invasive because of the need to dislocate the hip and cut through muscle surrounding the hip joint. Invasive procedures increase the trauma to the patient, the potential for complications, recovery time and the cost.
Replacement of the proximal portion of the femur is sometimes necessary due to degenerative bone disorders or trauma to otherwise healthy bone caused by accidental injury. In the latter instance it is desirable to replace the traumatized portion of the bone without causing further trauma to healthy bone. There is a need, therefore, for an implant that replaces a traumatized portion of the femur, but also significantly minimizes stress to the remaining healthy bone and that can be implanted by a method that is less invasive.
There are several other significant remaining problems and issues relating to hip arthroplasty. They include:
The Young, Active Patient:
Younger patients are more likely to have failure of their primary arthroplasty both due to increased demand on the mechanical construct, and from a pure life expectancy standpoint. It follows that they are more likely to require a revision and a second revision, which may lead to a catastrophic bone loss situation.
Instability:
This problem still occurs at the same rate that it did 50 years ago. Larger femoral heads may decrease the incidence, but no other significant technical changes have occurred to effect the incidence of this serious complication.
Bone Loss:
The overwhelming majority of present successful femoral prosthesis achieves fixation at least as far distal as the proximal femoral metaphysis. When these prosthesis fail, the next step usually involves diaphyseal fixation, often with a large diameter stiff stem.
Leg Length Inequality:
Leg length inequality after hip arthroplasty has always been a problem and an average lengthening of the leg of 1 centimeter is common. Lengthening is sometimes accepted for the sake of improved stability. Leg length inequality has been reported as the number one reason why surgeons are sued after hip arthroplasty
Surgical Morbidity:
Hip arthroplasty usually involves significant blood loss, body fluid alterations and pain. Shortly, it""s a big operation that hurts. It should be the goal of every compassionate surgeon to minimize these issues. If the operation can be made smaller, with less blood loss and less pain without diminishing long term results, every effort should be made to do so.
It would therefore be desirable to provide a femoral next prosthetic apparatus that overcomes these significant disadvantages.
It is therefore one object of the present invention to provide an improved apparatus and method for hip replacements.
It is another object of the present invention to provide an improved and less-invasive prosthetic which replaces the femoral head while retaining a substantially intact femoral neck.
The foregoing objects are achieved as is now described. The preferred embodiment provides a femoral neck fixation prosthesis and method of using same which reduces bone loss and avoids the other shortcomings of the prior art by allowing the fixation of a stable femoral head replacement while reducing the amount of the femur which must be reamed for the insertion of the prosthesis. The preferred embodiment provides that the femoral head is attached to a fixation prosthesis which extends coaxially through the central canal of the femoral neck, into the femur, and is then attached to the opposite lateral wall of the femur. In this manner, the prosthesis serves to imitate the original structure of the femoral neck. No other support members, either crosspins or arms extending into the length of the femur, are required.
The above as well as additional objectives, features, and advantages of the present invention will become apparent in the following detailed written description.